Objectives Evaluate blood and soft tissue in adult and geriatric monkeys previously exposed to lead. Compare these biomarkers with behavioral endpoints. Validate K X-ray-fluorescence measures of lead exposure. Most of the diagnosis of lead exposure is done by measuring the amount of lead present in blood. While this is a good way to diagnose current exposure, lead will only circulate in the blood for about 30-45 days after exposure ends and will not lead to an accurate account of past exposure. Since lead is stored in the bone, the best way to determine exposure is to get a measurement of what is still stored in the bone. The development of the K X-ray technique has enabled us to get a non-invasive in vivo measurement of total lead present. We are developing the technique and measuring bone lead levels in adult and in geriatric monkeys. These measures are compared with behavioral endpoints and other biological markers of lead exposure. Key Words Lead, Monkeys, Diet, K x-ray